Thread: Wobbly: my first 3-axis router
My goal with this machine is to be able to make parts in thin plywood and composites. First project is a gyro stabilised camera gimbal mount for my quadrocopter.
Detailed design is finished. Parts are beginning to arrive. I understand using ground axles for linear motion increase the risk of resonance. So I came up with the name 'Wobbly'!
Drive is through M12 threaded rods with anti-backlash nuts. In an attempt to unload motor axles I intend to use thrust bearings and lock nuts to support the rods in the frame.
Dimensions comes from using available cheap(er) parts like axles of a given length et cetera. Frame parts are MDF.
It is a prototype and the idea is to make all the electronics and logic work in a simple machine before moving to larger sizes and better linear motion.
Hope to start cutting MDF parts in a week or two. As usual, build start slipped a couple of weeks since parts are a little late...
What do you think?
Some screen shots:
The reason for building my CNC: gimbal camera mount:
First 1.75mm pitch is far to small and slow for cutting materials like MDF or plastics etc. This will severely restrict feed rates which will cause burning and quickly wear tools out in MDF and composites with melting in plastics.
Second the pitch of threaded rod is not consistent across it's length so accuracy will be all over the place.
Third the quality of thread on Normal threaded rod is rubbish and the roughness wears nuts out very quickly.
By the time you have messed around buying threaded rod and Delrin etc for Lead nuts it's just not worth taking that route and the little difference to buy decent Screws, whether that be Lead or Ballscrew is most certainly worth it from the beginning.
If you want a very accurate alternative slightly more expensive then use timing belt. It will give far greater feed rates and be very very accurate.
Also drop the unsupported linear rails they are rubbish. Go with supported has they don't cost much more and you can transfer to a better machine when you realise just how RUBBISH MDF for a CNC machine frame and build another with steel or aluminium.!!
That last bit should tell you everything about what I think to MDF for the Frame.!!
14-01-2013 #3Also drop the unsupported linear rails they are rubbish.
timing belts are definitely worth exploring though as the M12 like jazz says are likely to be an insurmountable bottle neck
Well, it's never too late to change one's mind. Found a very good deal on a pair of supported rails and some ballscrews. Therefore I redesigned my X-axis with the new linear bearings and all axis with b-screws.
Y- and Z-axis retain the ground axle with closed linear bearings.
Still waiting for the major components.
I've seen rails mounted this way. Are there any problems with mounting them vertically?
Thr red shaded area shows how much load in each direction supportted rail will take. In your situation I think you will be fine, the machine will probably rip through the mdf gantry a long time before you encounter a force that causes a problem with the rails.
Edit to add: You really need to rethink your spindle mount, it is far too weak. You need to make two of them that grip the spindle and put a few inches between them.
Do a google image search for: cnc spindle mount
and you will find plenty of examples to suit all budgets.
Last edited by D.C.; 18-01-2013 at 02:27 PM.
Yes, the spindle mount needs improving. The mount in the picture is made of aluminium but I intend to ad a support higher up. Just received my router (with mount) yesterday so I'll start design on the upper support soon.
What spindle & motors are you fitting to this machine ? As you have said the spindle will need much more support than you have with just that thin bracket. Where is the machine going to be kept because moisture is a big problem with MDF so needs to be sealed properly.
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